Concept 8.1: Photosynthesis uses light

energy to make food

I. I. The structure of ChloroplastsThe structure of Chloroplasts

The structure where photosynthesis The structure where photosynthesis takes place is the chloroplast.takes place is the chloroplast.

Chloroplasts contain compounds called Chloroplasts contain compounds called pigment that give leaves their color.pigment that give leaves their color.

Leaves contain the most chloroplasts.Leaves contain the most chloroplasts. There are tiny pores called stoma that There are tiny pores called stoma that

allows carbon dioxide to enter and allows carbon dioxide to enter and oxygen to leave the cell.oxygen to leave the cell.

I. I. The structure of ChloroplastsThe structure of Chloroplasts Veins carry CO2 and H2O from the plants Veins carry CO2 and H2O from the plants

roots to the leaves and deliver organic roots to the leaves and deliver organic compounds to other parts of the plant.compounds to other parts of the plant.

The inner membrane of a chloroplast The inner membrane of a chloroplast encloses a thick fluid called stroma.encloses a thick fluid called stroma.

Suspended in the stroma are many disk Suspended in the stroma are many disk shaped sacs called thylakoids which are shaped sacs called thylakoids which are arranged in stacks called grana.arranged in stacks called grana.

These stacks organize the series of These stacks organize the series of reactions that make up photosynthesis.reactions that make up photosynthesis.

PhotosynthesisPhotosynthesis

II. II. Overview of PhotosynthesisOverview of Photosynthesis

In cellular respiration, electrons “fall” In cellular respiration, electrons “fall” from glucose to O2 to release energy.from glucose to O2 to release energy.

In photosynthesis, electrons from water In photosynthesis, electrons from water are boosted “uphill” by the energy of are boosted “uphill” by the energy of sunlight.sunlight.

III. III. The Light ReactionsThe Light Reactions These excited electrons, along with carbon These excited electrons, along with carbon

dioxide and hydrogen ions produce C6H12O6 dioxide and hydrogen ions produce C6H12O6 moleculesmolecules

Photosynthesis occurs in two main steps: Light Photosynthesis occurs in two main steps: Light Reaction and Calvin Cycle (Dark Reaction).Reaction and Calvin Cycle (Dark Reaction).

The Light Reactions…con’tThe Light Reactions…con’t Light Reactions convert the energy in sunlight Light Reactions convert the energy in sunlight

to chemical energy.to chemical energy. Chloroplasts use captured light energy to Chloroplasts use captured light energy to

remove electrons from H2O, splitting it into remove electrons from H2O, splitting it into oxygen and hydrogen ions. oxygen and hydrogen ions.

The electrons and hydrogen ions are used to The electrons and hydrogen ions are used to make NADPH, which is an electron carriermake NADPH, which is an electron carrier

Chloroplasts also use the captured light energy Chloroplasts also use the captured light energy to generate ATP.to generate ATP.

The overall result of the light reactions is the The overall result of the light reactions is the conversion of light energy to chemical energy conversion of light energy to chemical energy stored in NADPH and ATP.stored in NADPH and ATP.

IV. IV. The Calvin CycleThe Calvin Cycle

Calvin Cycle makes sugar from the Calvin Cycle makes sugar from the atoms in carbon dioxide plus the atoms in carbon dioxide plus the hydrogen ions and high energy electrons hydrogen ions and high energy electrons carried in NADPH.carried in NADPH.

The ATP made in the light reactions The ATP made in the light reactions provides the energy to make sugar.provides the energy to make sugar.

The Calvin Cycle is sometimes referred The Calvin Cycle is sometimes referred to as the “light-independent reactions” to as the “light-independent reactions” because it does not require light energy because it does not require light energy to begin.to begin.

Concept 8.2 The Light Reactions Concept 8.2 The Light Reactions Convert Light Energy to Convert Light Energy to

Chemical Energy Chemical Energy

I. I. Light Energy and PigmentsLight Energy and Pigments

Light is a form of energy that travels in waves Light is a form of energy that travels in waves and the distance between adjacent waves is and the distance between adjacent waves is called a wavelength.called a wavelength.

The range of wavelengths is called the The range of wavelengths is called the electromagnetic spectrum.electromagnetic spectrum.

Visible light only makes up a small portion of Visible light only makes up a small portion of the electromagnetic spectrum.the electromagnetic spectrum.

II. II. Pigments and ColorPigments and Color

A substances color is due to chemical A substances color is due to chemical compounds called pigments.compounds called pigments.

Waves of light shining on a material can be Waves of light shining on a material can be absorbed, transmitted or reflected.absorbed, transmitted or reflected.

Leaves absorb blue-violet and red-orange light Leaves absorb blue-violet and red-orange light very well but either reflect or transmit green very well but either reflect or transmit green light and that is why leaves look greenlight and that is why leaves look green

III. III. Identifying Chloroplast Identifying Chloroplast PigmentsPigments

Using a technique called Using a technique called chromotography different pigments chromotography different pigments in a leaf can be observed.in a leaf can be observed.

Chlorophyll a absorbs mainly blue-Chlorophyll a absorbs mainly blue-violet light while chlorophyll b violet light while chlorophyll b absorbs mainly red light.absorbs mainly red light.

IV. IV. Harvesting Light EnergyHarvesting Light Energy Within the thylakoid membrane, chlorophyll and Within the thylakoid membrane, chlorophyll and

other molecules are arranged in clusters called other molecules are arranged in clusters called photosystems.photosystems.

Each photosystem contains a few hundred Each photosystem contains a few hundred pigment molecules, including chlorophyll a and pigment molecules, including chlorophyll a and b as well as carotenoids.b as well as carotenoids.

Each time a pigment molecule absorbs light Each time a pigment molecule absorbs light energy electrons are raised from a “ground energy electrons are raised from a “ground state” to an “excited state” state” to an “excited state”

Concept 8.3: The Calvin Concept 8.3: The Calvin Cycle makes sugar from Cycle makes sugar from

carbon dioxidecarbon dioxide

A Trip around the Calvin CycleA Trip around the Calvin Cycle

The Calvin Cycle is the sugar factory within the The Calvin Cycle is the sugar factory within the chloroplasts.chloroplasts.

The starting material for the Calvin Cycle is The starting material for the Calvin Cycle is regenerated each time the process occurs, the regenerated each time the process occurs, the starting material is called RuBP, (a sugar with five starting material is called RuBP, (a sugar with five carbons)carbons)

Inputs for the Calvin Cycle are ATP, CO2 and Inputs for the Calvin Cycle are ATP, CO2 and NADPH. (from light reaction and air thus no light)NADPH. (from light reaction and air thus no light)

The cycles output is an energy rich sugar The cycles output is an energy rich sugar molecule called G3P which is not quite like molecule called G3P which is not quite like glucose but it used as the raw material to make glucose but it used as the raw material to make glucose as the plant needs to.glucose as the plant needs to.

A Trip around the Calvin CycleA Trip around the Calvin Cycle

II. Summary of PhotosynthesisII. Summary of Photosynthesis

The overall equation for photosynthesis is:The overall equation for photosynthesis is: 6 CO6 CO22 + 6 H + 6 H22O O C C66HH1212OO66 + 6 O + 6 O22

Carbon dioxide + water Carbon dioxide + water Glucose + Oxygen Glucose + Oxygen

The light reaction take place in the thylakoid The light reaction take place in the thylakoid membranes and convert light energy into membranes and convert light energy into chemical energy in the form of ATP and NADPH.chemical energy in the form of ATP and NADPH.

The light reactions use the reactant HThe light reactions use the reactant H22O and O and release the product Orelease the product O2.2.

The Calvin Cycle takes place in the stroma and The Calvin Cycle takes place in the stroma and uses ATP and NADPH to convert COuses ATP and NADPH to convert CO22 to Cto C66HH1212OO6.6.

Summary of PhotosynthesisSummary of Photosynthesis Photosynthesis is the first step in the flow of Photosynthesis is the first step in the flow of

energy through an ecosystem.energy through an ecosystem. Photosynthesis is the ultimate source of all the Photosynthesis is the ultimate source of all the

food that you eat and all the oxygen that you food that you eat and all the oxygen that you breathe.breathe.

Concept 8.4: Concept 8.4: Photosynthesis has a Photosynthesis has a

global impactglobal impact

I. The Carbon CycleI. The Carbon Cycle

The Carbon Cycle is the process by which carbon The Carbon Cycle is the process by which carbon moves from inorganic to organic compounds and moves from inorganic to organic compounds and back.back.

Through photosynthesis, producers convert Through photosynthesis, producers convert inorganic COinorganic CO22 to organic compounds. (ex: sugar) to organic compounds. (ex: sugar)

Cellular Respiration by both producers and Cellular Respiration by both producers and consumers return the COconsumers return the CO22 to the atmosphere. to the atmosphere.

No other chemical process matches the output of No other chemical process matches the output of photosynthesis.photosynthesis.

Earth’s plants and other photosynthetic organisms Earth’s plants and other photosynthetic organisms make up about 160 billion metric tons of organic make up about 160 billion metric tons of organic material per year.material per year.

II. II. Photosynthesis and Global ClimatePhotosynthesis and Global Climate

One organism may either produce or use a One organism may either produce or use a relatively small amount of COrelatively small amount of CO2,2, the total the total effect of all the organisms on Earth has a effect of all the organisms on Earth has a very large effect.very large effect.

COCO22 only made up 0.03% of the Earth’s only made up 0.03% of the Earth’s atmosphere before this century.atmosphere before this century.

COCO22 traps heat from the sun that would traps heat from the sun that would have otherwise escaped back into space, have otherwise escaped back into space, this property is known as the Greenhouse this property is known as the Greenhouse Effect.Effect.

Greenhouse EffectGreenhouse Effect

Photosynthesis and Global ClimatePhotosynthesis and Global Climate

The greenhouse effect keeps the The greenhouse effect keeps the average temperature on Earth about average temperature on Earth about 10 degrees warmer than it would be 10 degrees warmer than it would be otherwise.otherwise.

The amount of COThe amount of CO22 in the in the atmosphere is rising with no end in atmosphere is rising with no end in sight.sight.